Pre-programmed Failure Behavior using Biology-Inspired Structures

Core (filler) materials are key components of the sandwich panel and box-beams that are used in the design of lightweight structures. They perform a variety of elastic-range functions such as transferring and supporting working stresses and energy and collapse management. There is an increasing demand, however, for post-yield performance characteristics such as buckling control, impact toughness, and maintenance of component strength after damage. Low density is also an important consideration, as overall component mass is critical in most applications. These cellular solids need to perform well under normal working stress conditions, yet still resist damage from simple and unavoidable low velocity impacts. A new design approach is suggested by biological systems that have evolved for toughness and damage tolerance (bones, trees, plants, corals, etc.). These systems share the relatively low density cellular arrangements of common synthetic core materials, but also exhibit variable density gradients within the core. (Figures 1 and 2) This paper describes engineering design methods that are inspired by such biology. The result is that a design’s failure modes can be more effectively “designed-in”, controlling locations and amounts of failure. INTRODUCTION Biology serves as a very capable inspiration for the design of mechanical structures. Inspired by such biology, we are using interactive graphics and visualization methods to evaluate non-homogeneous microtruss structures. We are developing numerical approaches with spatial mapping of density variations and optimization strategies. Figure 2 shows volume renderings of trabecular bone. We have fabricated those volumes on a layered manufacturing system to test and observe their micro-behavior under stress. (Figure 3) We are now mimicking that inhomogeneity using novel distribution functions, such as the radial density functions shown here, and a variety of interactive graphics techniques. The result will be novel arrangements of microtruss core designs that optimize the damage tolerance and toughness of corefiller structures. Figure 1: Unstressed and stressed variable density structures. Figure 2: A: a core of trabecular bone. B: slab extracted from the core.